How to put in a brake booster and master cylinder on a 1989 ford motorhome

Check rear of Master Cylinder--If wet likely Master Cylinder Leaking and Booster Damaged. They Should be replaced as a mated pair. (for warranty) and brake lines removed and system bled.

The inside, large pin, that pushes out to the hydroboost, may have fallen out when you took off the booster. Also the pin from the booster to the master cylinder may have been stuck inside the hydroboost that you took out. Pull the master cylinder off. You will see that the large shaft/pin is missing. Good luck.

The subdued sound of a burst of air is a sign the vacuum servo or booster is functioning as it should. For most people most of the time a power booster and a vacuum booster are the same things - there are such things as various types of "power brakes" but they are in the world of specialised motoring and commercial and industrial vehicles.

I suggest you revisit each wheel brake and ensure they are all as the vehicle manufacturer intended and the front brakes are not dragging. If they are dragging when turned by hand while lifted on a jack something is clearly wrong. Try briefly releasing a fluid bleed nipple - if that improves matters the hydraulic system has residual pressure. If there is no improvement something about the brake isn't correct.

Once you have satisfied yourself everything is as it should be between the master cylinder and the ground you should ensure the brake pedal linkage is correctly adjusted and operating properly and finally before re-bleeding the hydraulics you should ensure a small clearance exists between the brake booster push rod and the master cylinder piston, about 8 to 10 thou inch is about right...

You should not have any fluid leaking.
1.The new master cylinder may have been manufacturer incorrectly, but unlikely. 2.Did you reuse the fluid tank or did it come with a new one? If you re-installed old tank, seal may have not seated correctly. 3. Did you tighten the brake lines correctly? 4. It may be that there was fluid that leaking into the booster from the old cylinder, and that fluid is now coming out of the booster with use. One indication would be if the reservoir tank is showing any fluid drop. If it is the problem is 1,2, or 3 above. Let me know what you find out by leaving a comment.
I hope this helps. Feel free to comment or ask further questions.

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The booster is working properly if the pedal goes down a little when starting the truck. Seems more like it's a master cylinder problem if it won't pump up.

REMOVAL & INSTALLATION Fig. 1: Disconnect the warning indicator at the master cylinder
Fig. 2: Remove the fluid to minimize the amount that would otherwise inevitably be spilled
Fig. 3: Unscrew the line fittings at the master cylinder
Fig. 4: Hold a rag under the fittings to keep fluid from dripping all over things
Fig. 5: Unbolt the master cylinder from the brake booster
Fig. 6: Remove the master cylinder from the vehicle and set it in a clean location

1. Disconnect the negative battery cable.
2. Apply the brake pedal several times to exhaust all the vacuum in the system.
3. Detach and cap the brake lines from the master cylinder.
4. If equipped, detach the brake warning indicator connector. NOTE: A turkey baster (tapered tube with a squeeze ball on top) works well for removing fluid from the reservoir (see photo).
   
5. Siphon off the fluid from the master cylinder reservoir to minimize spillage when lines are disconnected.
6. If applicable, disconnect and cap the Hydraulic Control Unit (HCU) supply hose at the master cylinder reservoir and secure in a position to prevent loss of fluid.
7. Unfasten the 2 nuts and lockwashers that attach the master cylinder to the brake booster.
8. Remove the master cylinder from the booster by sliding it forward and upward from the vehicle. To install:
   
9. Install a new seal in the groove in the master cylinder mounting face.
10. Position the master cylinder assembly over the booster pushrod and onto the 2 studs on the booster assembly.
11. Install the retaining nuts, then tighten to 18–25 ft. lbs. (24–34 Nm).
12. Uncap and connect the brake lines to the master cylinder. Tighten the front fitting to 16–21 ft. lbs. (21–29 Nm), and the rear fitting to 10–15 ft. lbs. (15–20 Nm).
13. Uncap and connect the HCU hose to the master cylinder reservoir fitting and secure with a hose clamp.
14. If equipped, connect the brake warning indicator.
15. Fill the master cylinder with Heavy Duty Brake Fluid C6AZ-19542-AA or equivalent DOT 3 brake fluid from a clean, sealed container. Bleed the entire brake system, as outlined in this section.
16. Connect the negative battery cable.
17. Operate the brake several times, then check for external hydraulic leaks.

1. Step 1 Mark the brake lines coming into and out of the master cylinder using masking tape and permanent marker.
   
2. Step 2 Orient the tube wrench so that it grabs the end of the nut by first sliding it over the brake line.
   
3. Step 3 Pull the brake lines out of the master cylinder.
   
4. Step 4 Unbolt the two bolts that hold the master cylinder to the brake booster.
   
5. Step 5 Slide the master cylinder off the brake booster.
   
6. Step 6 Remove the bolts that hold the brake booster to the firewall.
   
7. Step 7 Remove the cotter pin from the pin holding the back of the brake pedal to the master cylinder.
   
8. Step 8 Slide the brake booster to brake pedal pin out of the mounting bracket.
   
9. Step 9 Pull the brake booster off the firewall.
   
10. Step 10 Install the new brake booster. Installation is the reverse of removal.
    

You have to Remove the brake lines going to the cylinder, then remove the 2 nuts holding it to the brake booster.

Make sure u bench bleed the new master before you install, the new one should come with a bench bleed kit, u must attach the 2 hoses to both ports on the master cylinder where the brake lines connect to, then run the 2 hoses into the top of the reservor and fill it with fluid, use a screw driver and pump the master cylinder until you can see no air bubbles running through the hoses

if the booster is bad the pedal would be hard sounds like the e-brake is stuck take off the drums and make sure the arms are all the way back then did you adjust the rear brakes after changing the shoes

5 Inspect Brake Fluid Type Brake fluid loss or contamination 10 Inspect Master Cylinder (Brake System) Worn or leaking brake master cylinder. 11 Inspect Brake Power Booster Damaged booster vacuum line/check valve, or diaphram

Pretty simple repair.I even did this alone.
DO NOT disconnect the brake lines unless you are changing the master cylinder out with it. Unbolt the master cylinder and move it forward slightly. From inside the truck,unbolt the brake pedal from the rod, leave the pedal hanging. Remove the 4 bolts at the firewall that retain the booster.From outside the truck reach in and draw the old booster out.You may have to move the master cylinder up or down to clear the booster.
The rod to the brake pedal will come out with the booster,make sure you put it back on the new one.

Reverse to install.

good luck
Dave